As stated above, the purpose of phase shifters is to control the phase difference, using the physical principle of the electrical delay produced in transmission lines to adjust the signal phase. The electrical delay can be obtained by various methods, such as those mentioned below.
One of said methods, as described in patent JP5121902 A, published on 18 May 1993, consists of modifying the propagation velocity of the transmission line, so that the phase shifter comprises a mobile dielectric part interposed between two coaxial conductors. The relative movement of this dielectric part changes the relative phase between the two conductors. One of the drawbacks of such a system is the variation in the characteristic impedance as the dielectric moves.
Another method used to obtain an electrical delay is that described in patent JP5121915 A, published on 28 May 1993, where the phase shifter disclosed has a transmission line that is mobile with respect to a fixed transmission line. The mobile line is connected to the phase shifter feed and is coupled to the fixed line, so that when it moves, the signal phase on one end of the fixed line will change with respect to the other end.
A similar system is described in patent JP9246846 A published on 19 Sep. 1997. This invention describes a phase shifter having three transmission line segments with a stripline construction, a circular shape and staggered in a peripheral sense, a connection point being adjusted around a central point in contact with the corresponding line segment.
European Patent EP1208614 B1, published on 1 May 2004, describes a phase shifter improved with respect to previous ones having one input and four outputs for connecting four radiating elements by pairs. It is provided with two stripline segments arranged concentrically and one feed element common to the two segments placed radially, said common feed element being able to revolve about a central axis to allow modifying the relative differences of the signal phase between the ends of the stripline segments.
This system has several drawbacks. On one hand, if the striplines exceed a certain length, resonances appear due to excitation of higher modes, so that after this length the phase shifter no longer works properly.
This is, the limitation in the use of striplines after a certain length limits the range of variation of the pointing angle.
For example, at 2170 MHz in order to displace by 8 degrees the direction of radiation of the array, the inner stripline must have an approximate length of 45 mm and a curvature radius to allow construction of about 31 mm. In turn, for a low coupling between lines the radius of the outer stripline must be about 62 mm and its length about 90 mm. With these dimensions, the resonant frequency appears around 2335 MHz. This implies that the maximum mechanical angle between end positions of the phase shifter must be approximately 83 degrees. For greater angles the phase shifter would not work, as the resonant frequency would fall inside the band. FIG. 2 of patent EP1208614 B1 is thus only valid when the angle is smaller than 83 degrees, and FIG. 4 will only be valid for an even smaller angle given its obvious larger size.
Another disadvantage of the striplines of said invention is their low mechanical rigidity, more so if the dielectric used is air, as said striplines lack any support to minimise vibrations or sagging. This is an important factor, as vibrations, sagging or deformations of striplines can lead to losses or variations in the voltage standing wave ratio (VSWR).
Another drawback of current mechanical phase shifters is the impossibility of actuating several common feeds of different phase shifters, requiring control by a single actuator.
In addition, the matching of the input signal transmission line to a specific impedance is performed externally to the phase shifter with cable lengths of different characteristic impedance and/or with impedance matching circuits, which increases the cost and complexity of the assembly.
Therefore, the object of the present invention is to provide a broad band mechanical phase shifter that overcomes the aforementioned drawbacks and therefore:                Provides a pointing angle range that is not so limited by the appearance of resonances because the L-lines may have a greater length than the striplines.        
Allows the striplines to be replaced by L-lines to thereby have a sufficient mechanical rigidity, more so considering that it is desired to increase their length in order to obtain a greater range of the pointing angle.                Allows the phase shifters object of the invention to be stacked such that all common feeds of the various phase shifters can be actuated simultaneously by acting jointly on their common rotation shaft.        Allows, by the design and configuration of the phase shifter, an improved assembly and mounting on the antenna as well as the use of 50 ohm cable exclusively in the entire antenna, with the resulting cost reduction        A reduction in costs and a simpler assembly of the antennae as relates to adjusting the impedance of the external input and output transmission lines of the phase shifter.        